Hiddekel

Called by the Accadians id Idikla; i.e., “the river of Idikla”,
the third of the four rivers of Paradise (Gen. 2:14). Gesenius
interprets the word as meaning “the rapid Tigris.” The Tigris
rises in the mountains of Armenia, 15 miles south of the source
of the Euphrates, which, after pursuing a south-east course, it
joins at Kurnah, about 50 miles above Bassorah. Its whole length
is about 1,150 miles.